PhoY2 but not PhoY1 is the PhoU homologue involved in persisters in Mycobacterium tuberculosis

Objectives: Mycobacterial persistence is thought to be the underlying cause of the current lengthy tuberculosis therapy and latent infection. Despite some recent progress, the mechanisms of bacterial persistence are poorly understood. We have recently identified a new persister gene phoU from Escherichia coli and have shown that the phoU mutant has a defect in persisters. The objective of this study is to evaluate the role of two phoU homologues phoY1 and phoY2 from Mycobacterium tuberculosis in mycobacterial persistence. Methods: M. tuberculosis phoY1 and phoY2 mutant strains were constructed. The persister-related phenotypes of the phoY1 and phoY2 mutants were assessed in vitro by MIC testing, drug exposure assays and also by survival in the mouse model of tuberculosis infection. Results: We demonstrated that M. tuberculosis PhoY2 is the equivalent of E. coli PhoU in that inactivation of phoY2 but not phoY1 caused a defect in persistence phenotype as shown by increased susceptibility to rifampicin and pyrazinamide in both MIC testing and drug exposure assays and also reduced persistence in the mouse model. Conclusions: This study provides further validation that PhoU is involved in persistence not only in E. coli but also in M. tuberculosis and has implications for the development of new drugs targeting persisters for improved treatment.